A web page is a document file created for display on the World Wide Web and web browsers. A web browser displays a web page on a monitor or mobile device. The web page is what displays, but the term also refers to a computer file, usually written in hypertext mark-up language (HTML) or other mark-up language. Web browsers coordinate the various web resource elements for the written web page, such as style sheets, scripts, and images, to present the web page.
Cascading Style Sheets (CSS) is an example of a style sheet language standard used for describing the presentation of a document written in a markup language, often used to set the visual style of a web page and user interfaces. A style sheet specification describes a priority scheme to determine which style rules apply if more than one rule matches against a particular element. In this so-called cascade, priorities (or weights) are calculated and assigned to rules, so that the results are predictable. CSS, HTML and JavaScript™ are commonly used by web page designers to create visually engaging webpages, user interfaces for web applications, and user interfaces for many mobile applications. (JAVA and all JAVA-based trademarks and logos are trademarks or registered trademarks of Oracle and/or its affiliates.)
Style sheet specifications are designed primarily to enable the separation of document content from document presentation, including aspects such as the layout, colors, and fonts. This separation can improve content accessibility, provide more flexibility and control in the specification of presentation characteristics, enable multiple HTML pages to share formatting by specifying the relevant style sheet data in a separate file (for example, a “.css” file), and reduce complexity and repetition in the structural content.
Separation of formatting and content makes it possible to present the same markup page in different styles for different rendering methods, such as on-screen, in print, by voice (via speech-based browser or screen reader), and on Braille-based tactile devices. It can also generate the display of a web page differently depending on the screen size or viewing device. Readers can also specify a different style sheet, such as another style sheet file stored on their own computer, to override one specified by an author or designer of a web page.